Composition and method for rendering silver surfaces tarnish resistant

ABSTRACT

ELEMENTAL SULFUR IN FINELY DIVIDED FORM IN A SILVER POLISH RENDERS A SILVER SURFACE TO WHICH THE POLISH IS APPLIED RESISTANT TO TARNISHING.

U.S. Cl. 106-10 3 Claims ABSTRACT OF THE DISCLOSURE Elemental sulfur infinely divided form in a silver polish renders a silver surface to whichthe polish is applied resistant to tarnishing.

DISCLOSURE This invention relates to rendering silver surfaces tarnishresistant, and more particularly to a silver polish for both cleaningand polishing tarnished silver surfaces and rendering them tarnishresistant.

Polishes for removing tarnish from silver surfaces are widely employed.They are usually in the form of a paste or a liquid suspension, bothcomprising essentially a liquid carrier, and an abrasive powder in suchfinely divided form and of such hardness that it will not scratch asilver surface. Hence, when the composition is applied to and rubbedover the silver surface, the tarnish is removed by the abrasive.Suitable emulsifying and protecting agents, and organic solvents mayalso be employed in the polish, as is exemplified in the US. patents toAvedikian 2,691,593, Murphy Re. 24,819, and Aler et al. 3,117,012. Thesepatents also disclose as antitarnish or tarnish resistant agentsincorporation of long chain organic sulfur compounds in the polish, suchas thioureas and thiols.

It has been found pursuant to this invention that elemental sulfur,namely free sulfur, possesses superior tarnish resistant properties inprecluding tarnishing of a silver surface which has been cleaned orpolished, for example, by a silver polish composition. Moreover, theinorganic sulfur is odorless and much less costly than the organicsulfur compounds of the aforementioned type which have an obnoxiousodor, particularly the thiols, and can be employed effectively in muchsmaller quantities, in the order of a few hundredths of a percent byweight of the composition.

Summarizing this invention, the elemental sulfur can be in any one ofvarious Well known forms, such as finely divided or powdered crystallinesulfur, amorphous sulfur in the form of a fine powder, colloidal sulfurWhich is inherently formed finely divided, flowers of sulfur which issublimed sulfur also inherently in fine powder form, milk of sulfur alsoknown as precipitated or colloidal sulfur or the so-calledwater-wettable sulfur of commerce.

On the polished silver surface, the elemental sulfur evidently reactswith the silver to form a very thin transparent substantiallymonomolecular film or layer of silver sulfide (Ag S) which issubstantially non-volatile, in contradistinction to the volatility oforganic sulfur compounds. Because of such non-volatility, the filmremains intact over a protracted period thus protecting the silveragainst tarnishing throughout such protracted period. At the same time,because of the thinness and transparency of the film, the lustre of thepolished silver will be visible therethrough.

The elemental sulfur need only be uniformly incor- Patented June 1, 1971porated in any type of silver polish. When such silver polish is appliedto a tarnished silver surface, the abrasive removes the tarnish film,and the elemental sulfur forms the protective film. After the polishingwith the silver polish, the silver may be wiped dry or washed or rinsedin the usual manner with water, usually warm water, but the silversulfide film will remain to protect the silver against tarnishing over aprotracted period.

If a silver surface has been polished by a polish not containing theinorganic sulfur hereof, an aqueous or solvent solution or suspension ofsuch sulfur can be applied over the polished surface, and it will formthe tarnish resistant protective film. Addition of wax to thecomposition apparently has a synergistic effect with the sulfur becausewhen wax is employed in the composition, tests have established that thefilm protection against tarnishing lasts for an even longer period as aresult of wax in the film.

From the preceding, it is seen that the invention has as its objects,among others, the provision of an improved silver polish compositioncontaining elemental sulfur as the essential component in providing atarnish resistant film on the silver surface after polishing thereof,which is substantially non-volatile and odorless in the composition, andcan be used effectively in small amounts, and the provision of animproved method for rendering a polished silver surface resistant totarnish. Other objects of the invention will become apparent from thefollowing more detailed description.

The silver polish can be of any suitable formulation comprising asessential components a fine silver nonscratching abrasive powder, and aliquid carrier in which the elemental sulfur is dissolved or uniformlysuspended. Desirably, the composition hereof also contains an organicsolvent immiscible with water as part of the liquid carrier, anemulsifying agent, and a protective colloid or suspending agent tominimize separation of the components. Wax is advantageously included inthe composition as wax has been found to enhance the tarnish resistanteffect, but wax may be omitted. The proportions of a suitable silverpolish containing elemental sulfur may be as follows in percent byweight:

Percent by Weight Liquid carrier 45-85 Protective colloid 0.01-0.3Emulsifying agent 1.5-5 Abrasive powder 8-30 Wax 05 Elemental sulfur0.0110

A minor proportion of carrier, which is essentially aqueous, may includean organic solvent.

With respect to the elemental sulfur, it will be noted that even arelatively small amount of at least 0.01 percent will serve to form atarnish resistant film. The maximum amount is relatively immaterial butamounts in excess of 10 percent by weight of the composition will serveno useful purpose and hence are not preferred. The most effective rangeof elemental sulfur in the composition is about 0.01 to 0.20 percent byWeight; and as previously related, the elemental sulfur can be in any ofits various forms.

When an organic solvent is employed to supplant some of the water, anysuitable solvent may be utilized, desirably liquid hydrocarbon typesolvents, such as odorless kerosene, naphtha, gasoline, odorless paintthinner or non-flammable solvents, such as chlorinated hydrocarbons, inthe boiling range from about 200 F. to 525 F. Such solvent is desirablewhen wax is in the composition as it dissolves the Wax, leaving a waxyfilm when the liquid evaporates. Generally, about 10 to 40 percent ofthe liquid carrier can be solvent.

As the protective colloid, any suitable suspending agent such as naturalgums, for example, gum tragacanth or gum arabic, may be employed.Synthetic gums, such as sodium carboxy methyl cellulose, ethoxycellulose gum or a hydroxyalkyl cellulose product may be employed, andalso any suitable aliginate thickening agent. As the wax, any suitabletype can be employed, such as microcrystalline wax, parafiin wax,vegetable wax, and mineral wax. Suitable emulsifying agents aredesirably non-ionic such as non-ionic detergents, or anionic, such asfatty acid soaps, or alkyl aryl sulfonates.

As the abrasive, the more finely divided the abrasive is, the better.Any of the well known abrasives may be employed in finely divided powderform so that it is nonscratching, such as fine charcoal, diatomaceousearth, precipitated chalk, or jewelers rouge, or mixtures of thesecomponents. Diatomaceous earth is the preferred abrasive of thefollowing particle size:

Microns: Percent Over 40 Zero 22-40 Trace -20 0.5 6-10 1.5 36 12 Lessthan 3 86 In formulating the composition, it is immaterial how theelemental sulfur is introduced into the composition as long as it isuniformly dispersed. The following is a typical formulation (andpreferred range variation) of a suitable composition containing fiowersof sulfur.

In making the composition, it is preferable first to disperse the smallamount of flowers of sulfur by stirring it in the odorless kerosene at atemperature of about 70 C. to 90 C., add the wax which dissolves in thekerosene upon continued stirring, then add this to warm water (about 70C. to 90 C.) containing the protective colloid and emulsifying agentdissolved or suspended therein, and agitate the components by stirrringto form a stable emulsion; and while the stirring is continued, addingthe abrasive gradually. The order of mixing is, however, not critical.The product is then allowed to cool to room temperature for filling insuitable containers.

The above polish may be applied to clean a silver surface in aconventional manner; and after cleaning of such surface the article isrinsed with warm water, leaving a waxy film of silver sulfide which issubstantially nonvolatile thus protecting the surface against tarnishingfor a protected period.

The elemental sulfur can be for-med in situ while the composition isbeing formulated by precipitating the same in the composition in anysuitable manner, such as by precipitation from a thiosulfate by an acid.

The following example is typical of a substantially similar formulationand the manner of making the same wherein the elemental sulfur is formedin situ from the following components in percent by weight:

Wax (parafiin wax. melting point 134 F.) Colloidal sulfur (estimated0.15%) formed by precipitation from:

Sodium thiosulfate (NagSzO fiHzO) 1. 19 1. 0-2 Sulfuric acid (H250 0 010 01-0. 02

Total -f 100];

In the above formulation, the precipitated or colloidal sulfur isprepared in situ by precipitation from sodium thiosulfate by the acid.In formulating the above composition, the order of mixing is notcritical. However, it is preferred that the solvent in which wax isdissolved be added to the essentialy aqueous carrier containing theother components after the colloidal sulfur has been formed therein. Thesulfur is desirably precipitated in the presence of the protectivecolloid in the water as this enhances dispersion and stability.

Thus, the sodium thiosulfate and concentrated sulfuric acid are addedwith agitation to the water containing the protective colloid at atemperature of about 70 to C. at which temperature the formation of theprecipitated sulfur is accelerated. After such precipitation, theemulsifying agent is added. The wax dissolved in the solvent, is thenadded with agitation to the aqueous colloidal sulfur dispersion, andfinally, the abrasive powder is added gradually under agitation afterwhich the composition is allowed to cool to room temperature and isfilled into suitable containers. The composition can be employed in thesame manner as described for Example I.

As previously related, although wax is advantageous, it need not beemployed, and the solvent need not be employed because the sulfur can beprecipitated from sodium thiosulfate with acid in situ in water at roomtemperature. The following is a typical example of such compositionwhich is formulated without application of heat:

EXAMPLE III The protective colloid is dissolved in the water at roomtemperature, and then the sodium thiosulfate is added to the water anddissolved at room temperature. After complete solution, the concentratedsulfuric acid is added thus effecting formation of colloidal sulfur; thereaction taking place slowly at room temperature under stirring. Theemulsifying agent is then added with stirring, after which the abrasiveis gradually added under stirring. Finally, the composition is filled insuitable containers and used in the manner described. The order ofmixing is not, however, critical.

Tests have established that the above compositions containing theelemental sulfur in even minute amounts, will resist tarnishing of afreshly polished silver surface at least twice as long as a popularsilver polish now on the market containing thiol compounds. Also, thecompositions hereof are easy to apply, and will not damage the silversurface polished, and are odorless in contrast to volatile organicthiols which have a marked unpleasant odor.

We claim:

1. The method of rendering a polished silver surface resistant totarnishing which comprises forming a substantially non-volatiletransparent film on said surface by applying to said silver surface acomposition containing free, elemental sulfur in finely divided form inan essentially aqueous carrier for the sulfur.

2. The method of rendering a polished silver surface resistant totarnishing which comprises forming a substantially non-volatiletransparent film on said surface by applying to said polished silversurface an essentially aqueous composition containing wax and free,elemental sulfur in finely divided form, the amount of said free,elemental sulfur in said composition constituting at least 0.01% byweight thereof.

3. The method of rendering a polished silver surface tarnish-resistant,which comprises forming a substantially non-volatile transparenttarnish-resistant film on said surface by applying thereto a compositioncomprising the following components in approximately the followingpercentages by weight:

Percent by weight Essentially aqueous carrier -85 Protective colloid0.010.3 Emulsifying agent 1.5-5 Wax 05 Silver non-scratching finelydivided abrasive powder 8-30 Elemental sulfur 0.0l10.0

References Cited UNITED STATES PATENTS 1,561,650 11/1925 Lashar 212.51,761,677 6/1930 Nielsen 10610X 1,766,646 6/1930 Jones 21-2.5 2,876,1483/1959 Singer 1486.24 3,226,180 12/1965 Irwin 212.5 3,345,295 10/1967Schwarcz et a1. 106-3XV DONALD J. ARNOLD, Primary Examiner J. B. EVANS,Assistant Examiner US. Cl. X.R.

